What you can do, if you do not have many plots, is to view them with jmol and then export them.

EDIT

From the Sage command-line, it is on the top of the window, you can export in .spt format from the jmol applet : FILE > Export > Write State

From the Sage notebook, click on the circular arrow (bottom left of the image) to let jmol start, then right click on the image, you will get a menu: with File > Save you can export as a JVXL isosurface, from File > Export, you can export as VRML and X3D 3D models.

I can't see the sage command line that you speak of. I am using cloud.sagemath though. I have managed to get jmol import of three.js objects to work. I think that in the screen rendering, three.js is involved.